Impact resistant vinyl ester resin and process for making same

ABSTRACT

Vinyl ester resins with improved impact resistance and other benefits and advantages may be obtained by a process modification wherein up to 20 percent of the unsaturated monocarboxylic acid, which is reacted with a polyepoxide, is replaced by an equivalent amount of a liquid carboxy terminated polydiene rubber capable of reacting with epoxy groups to form a chemically bound molecule. .Iadd.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of my copending application Ser. No.753,395 filed December 22, 1976, now abandoned, which, in turn, is areissue of Ser. No. 343,716 filed March 21, 1973, U.S. Pat. No.3,892,819. .Iaddend.

BACKGROUND .Iadd.OF THE INVENTION .Iaddend.

The preparation of a thermosettable vinyl ester resin by the reaction ofan unsaturated monocarboxylic acid such as methacrylic acid with apolyepoxide is known. While the physical properties of the cured resincan be varied depending on the choice of reactants, the choice ofmonomer copolymerizable with the resin and the like, the properties mayalso be modified by adding various materials to the resin. Inertreinforcing materials such as glass fibers and inert fillers such asCaCO₃ or kaolin clay are commonly employed both to improve propertiesand to reduce costs.

A variety of other additives are also known: thickening agents,thermoplastic low profile (smooth surface) additives, rubbery polymersto improve impact resistance, and the like. However, compatibility ofthese additives with the resin may frequently be a major problem whichcalls for other additives to stabilize the system. Some of theadditives, unfortunately, are also susceptible to removal from the curedresin by contact with solvents and the like. Consequently, theadvantages of certain additives may be lost or diminished in valuebecause of these problems.

It would be desirable to have a thermosettable resin that inherentlyprovides all of the desired properties. This ideal may never be reachedbut an object of this invention is to inherently provide improved impactresistance in the vinyl ester resin by chemically incorporating apolydiene rubber into the thermosettable resin itself. Other objects,benefits and advantages of the invention will become readily apparentfrom the description which follows.

SUMMARY

The objects and benefits of this invention are obtained by a modifiedprocess for making vinyl ester resins wherein a polyepoxide is reactedwith an unsaturated monocarboxylic acid and a liquid carboxy terminatedpolydiene rubber. The combined acid equivalents of said unsaturated acidand polydiene rubber ranges from about 0.8 to 1.2 equivalents perepoxide equivalent. At least about 80 percent of the acid equivalentscomprises the unsaturated acid and the balance between 0.01 and 20percent comprises the polydiene rubber, provided that the polydienerubber content of the resin is at least about 4 weight percent.

The novel vinyl ester resins are useful as powder coatings as well as inadmixture with copolymerizable monomers to prepare reinforced plasticarticles.

DESCRIPTION

Terminally unsaturated vinyl ester resins possess a number ofoutstanding properties which account for their commercial acceptance insuch areas as molding resins, corrosion resistant reinforced plasticpipe and other vessels, glass fiber laminates, and the like. But likemost thermosettable resins, vinyl ester resins do not possessoutstanding impact resistance.

While impact resistance of vinyl ester resins can be improved by addingcertain polydiene rubbers (see U.S. Pat. No. 3,674,893), it would bedesirable to avoid the need for such additives and provide the impactresistance as an inherent property of the resin. Additives to anythermosettable resin frequently result in other problems such asinstability, viscosity control and the like which can be avoided if theneed for the additive can be eliminated in the first place.

Vinyl ester resins are generally prepared by reacting together aboutequivalent amounts of an unsaturated monocarboxylic acid and apolyepoxide. An early patent U.S. Pat. No. 3,179,623, describes theabove reactions and resins. Further details about the resins, which arecalled vinyl ester resins herein, and conditions and methods of makingthem can be found in the following U.S. Pat. Nos.: 3,301,743; 3,317,465;3,377,406; 3,256,226 and 3,367,992. All the above patents areincorporated herein by reference.

Briefly, any of the known polyepoxides may be employed in thepreparation of the vinyl ester resins of this invention. Usefulpolyepoxides are glycidyl polyethers of both polyhydric alcohols andpolyhydric phenols, flame retardant epoxy resins based on tetrabromobisphenol A, epoxy novolacs, epoxidized fatty acids or drying oil acids,epoxidized diolefins, epoxidized diunsaturated acid esters as well asepoxidized unsaturated polyesters, so long as they contain more than oneoxirane group per molecule. The polyepoxides may be monomeric orpolymeric.

Preferred polyepoxides are glycidyl polyethers of polyhydric alcohols orpolyhydric phenols having equivalent weights per epoxide group of about150 to 1500, preferably about 250 to 700 and more preferred about 400 to600. Generally, as the epoxide equivalent weight decreases the amount ofcarboxy terminated rubber increases. The polyepoxides are characterizedby the presence of more than one epoxide group per molecule.

Unsaturated monocarboxylic acids include acrylic acid, methacrylic acid,halogenated acrylic or methacrylic acids, cinnamic acid and the like andmixtures thereof, and hydroxyalkyl acrylate or methacrylate half estersof dicarboxylic acids as described in U.S. Pat. No. 3,367,992 whereinthe hydroxyalkyl group preferably has from two to six carbon atoms. Saidacid is generally reacted with the polyepoxide in the proportions ofabout 1 equivalent of acid per each equivalent of epoxide, but theproportions of equivalents may range from about 0.8/1 to 1.2/1,respectively.

According to this invention improved impact resistance is obtained byreplacing up to about 20 percent of the equivalents of unsaturated acidwith an equivalent amount of a liquid carboxy terminated polydienerubber. By liquid it is meant to include the low molecular weightpolydienes of about 2000 to 20,000 molecular weight and preferably about3,000 to 10,000. Of the combined acid equivalents employed in theprocess at least about 80 percent comprises said unsaturated acid andthe balance between about 0.01 and 20 percent comprises said polydiene,provided that the polydiene rubber content of the resin is at leastabout 4 weight percent. By carboxy terminated is meant that thepolydiene rubber is terminated at each end with an acid carboxy, --COOH,group.

The particular liquid carboxy terminated polydienes used in thisinvention may be prepared by any suitable means. One procedure involvessolution polymerization of a conjugated diene monomer in the presence ofan organo metal catalyst. The lithium catalysts and in particular thedilithium catalysts such as dilithiobutane, dilithium stilbene,dilithium napthalene and the like are preferred. By employing dilithiumcatalysts the polymer obtained is terminated at each end by a lithiumatom. Treatment of said polymer with carbon dioxide replaces the lithiumatoms with carboxy lithium salt groups. As a final step the polymer istreated with acid to convert the lithium salt to the free acid form.Carboxy terminated polymers of various conjugated dienes or mixtures ofsame may be prepared in this manner. The conjugated dienes may have from4 to 12 carbon atoms and preferably from 4 to 8. Typical monomersinclude 1,3-butadiene, isoprene, piperylene, methylpentadiene,3,4-dimethyl-1,3 hexadiene and the like.

Also included within the definition of polydiene rubbers are carboxyterminated liquid copolymers of a conjugated diene and a copolymerizablevinyl monomer. Suitable monomers include alkenyl aromatics such asstyrene, vinyl toluene, α-methyl styrene etc.; nitriles such asacrylonitrile, methacrylonitrile, etc.; acrylate and methacrylate esterssuch as the methyl, ethyl, propyl, cyclohexyl etc. esters; heterocyclicnitrogen-containing monomers such as the various vinyl pyridine isomers,etc.; vinyl chloride, vinylidene chloride, methyl vinyl ether and thelike. Said copolymers should contain at least 40 weight percent of dieneand correspondingly from 0 to about 60 weight percent of at least onecopolymerizable vinyl monomer different from said diene monomer.

Preferred copolymer polydienes are the liquid carboxy terminatedacrylonitrile/butadiene copolymers and particularly preferred are thosecopolymers prepared from 12 to 25 percent acrylonitrile and 88 to 75percent butadiene.

The preparation of carboxy terminated polydienes is well known. U.S.Pat. No. 3,135,716 is typical of the art describing a process forpreparing terminally reactive polymers as well as the various reactionswhich may be employed to introduce different functional terminal groups.The disclosure of U.S. Pat. No. 3,242,129 is also typical of the art,especially the portions contained in columns 6-8 thereof. The above twopatents are incorporated herein by reference. Numerous other patentscould be cited but are considered unnecessary.

The vinyl ester resins typically are prepared in the presence ofcatalysts such as the organophosphonium salts, tertiary amines such as2,4,6-tri(dimethylaminomethyl) phenol [DMP-30] and the like. Variousvinyl polymerization inhibitors such as hydroquinone or its methyl etherand the like may be present during the reaction or added after the resinforming reaction. If desired the reaction may be run in an inertsolvent, preferably one which can be readily removed by evaporation etc.after the resin has been prepared. The carboxy terminated polydiene maybe reacted with the polyepoxide first followed by addition and reactionof the unsaturated monocarboxylic acid or both acid reactants may beadded and reacted with the polyepoxide at the same time.

The polydiene rubber modified vinyl ester resin produced hereintypically contains terminal polymerizable groups and associatedtherewith a hydroxyalkylene group, e.g. --CH₂ CH(OH)CH₂ --, formed bythe reaction of the acid carboxy group with the epoxide group. Thishydroxyl group may be used for further modification, e.g. by apost-reaction with a dicarboxylic acid anhydride in proportions up toabout 1 mole per equivalent of hydroxyl. A modification of this kind isdisclosed in U.S. Pat. No. 3,564,074. Other materials which are reactivewith hydroxyl groups, e.g. isocyanates, acyl halides, etc. may be usedto modify the vinyl ester resin.

Both saturated and unsaturated anhydrides are useful in said postreaction. Suitable dicarboxylic acid anhydrides containing ethylenicunsaturation include maleic anhydride, the halogenated maleicanhydrides, citraconic anhydride, itaconic anhydride and the like andmixtures thereof. Saturated dicarboxylic acid anhydrides includephthalic anhydride, tetrabromophthalic anhydride, chlorendic anhydride,anhydrides of aliphatic unsaturated dicarboxylic acid and the like.

The rubber modified vinyl ester resins are higher molecular weightresins by virtue of chemically combining the carboxy terminatedpolydiene rubbers into the resin structure. Accordingly, many of theresins are suitable as powder coating materials. A mixture of thepowdered resin with a peroxide or other catalyst may be readily cured atan elevated temperature. The pendant carboxyl groups are of importancein powder coatings since they can be reacted with metal oxides to makesolid powdered even in the presence of liquid monomers.

The resins are more commonly used in admixture with a copolymerizablemonomer to prepare laminates, glass reinforced plastic pipe, reinforcedmolded parts, and the like. The rubber modified vinyl ester resin may becombined with up to 60 to 70 weight percent of monomer. The proportionswill vary, somewhat depending on the monomer selected, other additivesemployed and other factors. A variety of copolymerizable monomers aredisclosed in the vinyl ester patents previously referred to. Typicalmonomers are styrene, vinyl toluene, halogenated styrenes, alkylsubstituted styrenes, alkyl substituted styrene, acrylic and methacrylicesters, hydroxyalkyl esters of acrylic and methacrylic acid, and thelike. More usually the monomer content will range from about 30 to 60weight percent.

The choice of monomer is also based on whether the resin is to be curedby thermal and/or chemical means or by high energy radiation. Withchemical catalysts (e.g. peroxides, persulfates, diazo compounds, etc.)and/or heat styrene is a common monomer because of its low cost andavailability as well as the properties obtained. However, to minimizethe radiation dosage needed to cure monomers other than aromaticmonomers may be employed such as butyl acrylate and hydroxyalkylacrylates.

As indicated, the rubber modified vinyl ester resin may be cured(thermoset) by various means. Cure accelerators such as the metalorganic acid salts, e.g. cobalt naphthenate, or tertiary amines such asN,N-dimethyl toluidine are frequently used with chemical catalysts.Sensitizers or photoinitiators which reduce the radiation dosage mayalso be employed with radiation, especially with ultra violet light.Other materials may be added to the resin such as inert reinforcingfibers, e.g. glass, asbestos, carbon, etc.; inert fillers such as kaolinclay, CaCO₃ etc.; mold release agents, thickeners, other pigments,thermoplastic low-profile additives, density reducers such as glass orphenolic microballons, blown saran microspheres and the like.

The improved impact resistance of the rubber modified vinyl ester resinsmakes the resin especially useful in coatings and for molded articles.Of particular interest are molded parts such as motor housings for powermowers, boats and recreation products, automotive parts such as panelsand housings, molded furniture containing blown saran microspheres whereimproved toughness and durability are required in medium densitysyntatic foams for chair legs and arms, doors, backup for acrylic facedbath tubs, lavatories, etc.

The invention will be further illustrated by the following non-limitingexamples. All parts and percentages are by weight unless otherwisespecified.

EXAMPLE 1

In a suitable reactor 455 parts of a glycidyl polyether of bisphenol Ahaving an epoxide equivalent weight (EEW) of 189 (D.E.R.331) was reactedwith 154 parts of bisphenol A in the presence of 0.5 part of t-butylphosphonium acetate at 150° C. The reaction exothermed to 190° C. andyielded a polyepoxide resin with an EEW of about 600.

After cooling the following were added to the reactor: 76 partsmethacrylic acid, 1.2 parts DMP-30 catalyst, 228 parts carboxyterminated copolymer of butadiene-acrylonitrile (82:18) containing 2.5%carboxy, --COOH(Hycar CTBN, Goodrich Chemical Co.) and 0.17 part ofhydroquinone. The reaction was continued at 120°-130° C. until thepercent carboxy of the resin was 1.15%. The resin was then poured out inthin sheets to cool. This resin contained about 25% of said rubber.Additional resins containing decreasing amounts of said rubber wereprepared in a similar manner, substituting an equivalent amount ofmethacrylic acid for the amount of the decrease in rubber content. Aportion of each of the resins was powdered, mixed with 1% dicumylperoxide, cured at 280° F. and post-cured at 100° C. for 30 minutes. Acontrol resin with no rubber was made for comparison purposes.

    ______________________________________                                               %        Heat Distortion                                                                            Notched Izod Impart,                             Resin  Rubber   264 psi      Ft-lb/inch                                       ______________________________________                                        A      0        184          0.3                                              B      5.8      176          0.4                                              C      11.1     166          0.4                                              D      15.7     157          0.5                                              E      25       140          1.02                                             ______________________________________                                    

As noted each of the uncured resins was non-blocking at 70° F. and couldbe powdered or flaked. Similar results are obtained if the copolymer isreplaced by an equivalent amount of a carboxy terminated polybutadiene.

Tests were also made with some of the resins diluted to 50% styrenemonomer. Clear castings were made by adding 1% benzoyl peroxide, curingat 100° C. for 1 hour and post-curing at 130° C. for 45 minutes.

    __________________________________________________________________________             Izod Notched                                                             Visc.,*                                                                            Impact %   HDT, °F.                                                                     Tensile                                                                           Flex. Str                                                                          Flex Mod                                   Resin                                                                             cps  Ft-lbs/in.                                                                           Elong.                                                                            264, psi                                                                            psi psi  psi × 10.sup.5                       __________________________________________________________________________    A    300(N)                                                                            0.380   9  215   11,000                                                                            17,300                                                                             4.3                                        D   2000(T)                                                                            0.595  25  174   7,170                                                                             11,900                                                                             3.2                                        E   2600(T)                                                                            0.563  25  124   4,000                                                                              5,700                                                                             2.1                                        __________________________________________________________________________     *N--newtonian;                                                                T--thixotropic                                                           

Additional tests were made with resin E in which an unmodified vinylester resin (prepared by reacting equivalent amounts of an epoxynovolac, D.E.N. 438, with methacrylic acid) diluted to 25% styrene wasblended therewith in varying amounts to vary the amount of rubber in thetotal resin. Clear castings were then made by curing with 1% benzoylperoxide (BPO) at 80° C. for 6 hours and post curing for 30 minutes at250° F. The casting at a 10% rubber level could be hammered and wasslightly malleable whereas at 2.5% rubber the castings were brittle andshattered easily.

EXAMPLE 2

Similar to example 1 a higher molecular weight polyepoxide was firstprepared by reacting 6.5 lbs of bisphenol A with 6.58 lbs of D.E.R. 736(an aliphatic diepoxide with an EEW of 175-205) in the presence oft-butyl phosphonium acetate catalyst. Then 4.05 lbs of a carboxyterminated butadieneacrylonitrile rubber similar to example 1, 6.97 lbsof methacrylic acid were added and reacted using a catalyst (DMP-30) andhydroquinone as an inhibitor. After the reaction was completed 36 lbs ofstyrene was added and mixed with the resin. The liquid resin had aviscosity of 57.7 cs.

The following molding formulation was prepared.

    ______________________________________                                        Resin                   100    parts                                          Nevada sand             37.5   parts                                          Milled glass fiber      25     parts                                          ASP-400 Kaolin clay     12.5   parts                                          Cab-O-Sil (silica)      0.5    parts                                          N,N--dimethylaniline (DMA)                                                                            0.4    parts                                          Cadox 40E (40% benzoyl)                                                       peroxide                5.0    parts                                          ______________________________________                                    

A pipe collar was molded directly into a 12 inch pipe using the aboveformulation at 150° F. The collar was demolded about 15 minutes afterthe formulation was accelerated with the DMA promoter. The collar wasaged for 24 hours and then tested for impact resistance. The collarpassed a 20 foot drop test without breaking.

Clear castings were also prepared from the resin using two differentcatalyst systems.

    ______________________________________                                                1% benzoyl peroxide                                                                         0.5% Co Naph                                                    0.2% DMA      1.5% MEK Peroxide                                       ______________________________________                                        Tensile, psi                                                                            6,820           5,940                                               Elongation, %                                                                             15              38                                                264 psi, HDT                                                                            120° F.  --                                                  ______________________________________                                    

EXAMPLE 3

Another group of resins was prepared by heating together in the presenceof a catalyst a polyepoxide or mixtures thereof, methacrylic or acrylicacid and a carboxy terminated butadiene/acrylonitrile rubber similar tothat used in example 1. Heating was continued until the carboxy contentreached a low value of less than 2%. Styrene monomer was then added.Clear castings were cured with 1% BPO and 0.2% DMA for one hour at 80°C. and post cured at 250° C. for 1 hour. The compositions of the resinsand their physical properties are recorded in the following tables.

    __________________________________________________________________________    Composition                                                                                                     Rubber                                      Resin                                                                             D.E.R. 331.sup.(1)                                                                   D.E.R. 732.sup.(2)                                                                   D.E.R. 741.sup.(3)                                                                   MAA.sup.(4)                                                                        AA.sup.(4)                                                                        Parts                                                                             %  Styrene                              __________________________________________________________________________    A   760    --     --     --   288 112 7  500                                  B   570    325    --     335  --  140 7  590                                  C   570    325    --     335  --  310 14 660                                  D   570    --     370    335  --  145 7  610                                  E   570    325    --     335  --   0  0  530                                  __________________________________________________________________________     .sup.(1) aromatic polyepoxide, EEW 186-192                                    .sup.(2) aliphatic polyepoxide, EEW 305-335                                   .sup.(3) mixture of aromatic and aliphatic polyepoxide, EEW 364-380           .sup.(4) MAA--methacrylic acid;                                               AA--acrylic acid                                                         

    ______________________________________                                        Properties                                                                    Izod Impact      Flexural                                                     Ft-lbs/inch      Strength,                                                                              Barcol   HDT, °F.                            Resin Unnotched Notched  psi    Hardness                                                                             264 psi                                ______________________________________                                        A     3.5       0.207    13,000 24     167                                    B     7.7       0.422     9,000 23     149                                    C     10.5      0.552     4,500  0     --                                     D     7.2       --       11,300 27     167                                    E     4.7       0.141    15,000 40     177                                    ______________________________________                                    

EXAMPLE 4

Variations in the previous examples may be made. The procedure ofexample 1 was changed by reacting the polyepoxide, the polydiene rubberand the bisphenol A together first at 140°-160° C. After cooling to 110°C. the methacrylic acid was added and reacted. The epoxy and the rubbermay be combined first and heated followed by addition of the bisphenol Aand heating until desired epoxide equivalent weight is produced. Otherpolyepoxides which were used in the preparation of the vinyl esterresins of this invention included an epoxy novolac (D.E.N. 431) with anEEW of 172-179 and flexible polyepoxides with an EEW of 305-335 (D.E.R.732) and 364-380 (D.E.R. 741). The CTBN rubbers may be replaced by anequivalent amount of any of the commercial carboxy rubbers such asButarez CTL I and II (Phillips Petroleum), Telogen CT (General Tire &Rubber Co.) or HC-434 (Thiokol Chemical Co.).

EXAMPLE 5

The polydiene rubber modified vinyl ester resins have improved adhesiveproperties as well as impact resistance. Resins A, D and E of example 1were used. In addition Resin A (0% rubber) was physically blended withthe polydiene rubber used in preparing Resin D and E to a 12.5% rubberlevel. All resins were diluted to 50% styrene.

An adhesive formulation with each resin was prepared by blending 20parts per 100 parts of resin (phr) of MD-101 aluminum powder and 1 phrbenzoylperoxide. Lap shear specimens were prepared according toASTM-1002 using chromate etched aluminum strips, 1×4×0.064 inches. Theadhesives were cured at 250° F. for 30 minutes and after cooling lapshear values were determined.

    ______________________________________                                                    Percent Polydiene                                                                          Lap Shear                                            Resin       Rubber       psi                                                  ______________________________________                                        1,A         0            3270                                                 1,D         7.7          4980                                                 1,E         12.5         3635                                                 Blend*      12.5          325                                                 ______________________________________                                         *Blend of rubber and Resin 1,A.                                          

The improvement is apparent and is particularly evident over the blendedresin where the added rubber detracted from the lap shear value.

EXAMPLE 6

Carboxy rubber modified vinyl ester resins were compared to comparableresins without said rubber. McGarey cleavage tests were made bypreparing test bars 6×1.2×0.25 inches in which a lengthwise cut was madeon each side of the bar to one-third the thickness of the bar. At oneend an initial 1 inch cut was made all the way through the bar to helpinitiate splitting. In each case the resin was cured with 1% benzoylperoxide catalyst for 6 hours at 80° C. followed by 45 minutes at 250°F.

The test bars were then split the length of the cut obtaining astress-strain curve. Stress was applied at a rate of 0.05 inches perminute. The area under the plotted curve was taken to be representativeof the work required to form the new split surface. At the same styrenelevel the test bar with no rubber content in the resin had an area underthe stress-strain curve of 190 whereas the carboxy polydiene rubbercontaining resin had an area of 2350. The split in the latter case alsoshowed a great deal of stress whitening along the crack propagation linewhich is an indication of toughness.

What is claimed is:
 1. A process for preparing a thermosettable resinhaving improved impact resistance in the thermoset state which comprises.[.simultaneously.]. reacting the epoxide moieties of a polyepoxidehaving an average of more than one epoxide group per molecule with theacid moieties of an unsaturated monocarboxylic acid and a liquid carboxyterminated polydiene rubber wherein the combined acid equivalents ofsaid unsaturated acid and said polydiene ranges from about 0.8 to 1.2equivalents per epoxide equivalent and wherein at least about 80 percentof said acid equivalents comprises said unsaturated acid and the balancebetween 0.01 and 20 percent comprises said polydiene, provided that thepolydiene rubber content is at least about 4 weight percent .Iadd.andwherein said resin is prepared by the simultaneous reaction of saidpolyepoxide, said polydiene rubber and said monocarboxylic acid or bythe sequential reaction wherein said polyepoxide and said polydienerubber are reacted followed by addition and reaction of saidmonocarboxylic acid with the product of that first reaction.Iaddend.. 2.The process of claim 1 wherein said polydiene rubber has a molecularweight of 2,000 to 20,000.
 3. The process of claim 1 wherein saidpolydiene rubber molecular weight is 3,000 to 10,000.
 4. The process ofclaim 1 wherein said polydiene rubber is a polymer of a conjugated dienemonomer.
 5. The process of claim 1 wherein said polydiene rubber is acopolymer of a conjugated diene and a copolymerizable vinyl monomer. 6.The process of claim 1 wherein said polydiene rubber is a copolymer ofacrylonitrile and butadiene.
 7. The process of claim 1 wherein saidpolyepoxide has an epoxide equivalent weight of 250 to
 700. 8. Theprocess of claim 1 further comprising the step of admixing thethermosettable resin with a copolymerizable monomer.
 9. A thermosettableresin prepared by the process of claim
 1. 10. A thermosettable resinprepared by the process of claim
 2. 11. A thermosettable resin preparedby the process of claim
 3. 12. A thermosettable resin prepared by theprocess of claim
 4. 13. A thermosettable resin prepared by the processof claim
 5. 14. A thermosettable resin prepared by the process of claim6.
 15. A thermosettable resin prepared by the process of claim
 7. 16. Athermosettable resin prepared by the process of claim 8.